The Keeling Curve

The Scripps CO2 measurements at Mauna Loa have been supported for many years by the U.S. Department of Energy (DOE), and have more recently been supplemented by Earth Networks, a technology company that is collaborating with Scripps to expand the global GHG monitoring network. Support for website development was provided in part by the National Science Foundation (NSF). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of NSF.

The rate of growth in carbon dioxide concentrations in the atmosphere has accelerated since the beginnings of the Keeling Curve. The rate has gone from about 0.75 parts per million (ppm)/yr in 1959 to about 2.25ppm/yr today. The attached graphic is from the Intergovernmental Panel on Climate Change Fifth Assessment Report and is based on data gathered by the Scripps CO2 Group and NOAA. The lower image shows the growth rate versus time, which has consistently stayed in positive territory since the late 1950s. No surprise here, because Mauna Loa record shows a clear rise from year to year. But this plot also shows that the growth rate (while staying positive) does vary quite a bit from year to year, something that is less evident in the Mauna Loa record. These variations are due to a combination of natural and human factors.

The Mauna Loa carbon dioxide (CO2) record, also known as the “Keeling Curve,” is the world’s longest unbroken record of atmospheric carbon dioxide concentrations. This record, from the NOAA-operated Mauna Loa Observatory, near the top of Mauna Loa on the big island of Hawaii, shows that carbon dioxide has been increasing steadily from values around 317 parts per million (ppm) when Charles D. Keeling began measurements in 1958, to nearly 400 ppm today.

Scientists make CO2 measurements in remote locations to obtain air that is representative of a large volume of Earth’s atmosphere and relatively free from local influences that could skew readings. The quality of data is verified before daily average values are determined.